Vibratory process equipment is used in a wide variety of industrial applications. Vibratory feeders and conveyors, for example, may be used to transport granular material, foundry castings, or other objects. Such feeders and conveyors typically include a bed on which the objects are transported and a drive for producing a vibratory motion of the bed which advances the objects in the desired direction. The drive typically includes an electric motor with eccentric weights mounted on the output shaft. In operation, the output shaft with eccentric weights is rotated to generate vibratory force that is transferred to the bed.
Vibratory process equipment may be classified by the number of non-rigidly coupled masses used to generate the vibratory motion. As such, systems are known that may be classified as one, two, or three mass systems. In single mass systems, the drive is rigidly connected to the bed and the drive/bed combination is isolated from surrounding terrain by an elastic member. In two or three mass systems, the drive is elastically coupled to the bed, and either the drive or the bed is isolated from surrounding terrain by an elastic member, which may be preferable in many applications since they are capable of more efficiently producing vibratory movement. Consequently, a smaller motor may used be used in a two-mass system to produce a force having the same amplitude as that of a single-mass system having a larger motor.
The conventional rotating motors produce a rotational force that may have an unnecessary and undesired force component. Various types of vibratory process equipment require a bed to be driven in a desired direction. The rotational force produced by rotating eccentric weights, however, generates a force component that is perpendicular to the desired direction. In addition, for two mass systems, the drive is coupled to the bed by an elastic member that is not restricted as far as the direction in which it is excited. More specifically, the elastic member will typically have several degrees of freedom in which it may be excited. A coil spring, for example, has six primary degrees of freedom (i.e., movement along the X, Y, and Z axes and rotation about the X, Y, and Z axes). Each degree of freedom may have a resonant frequency associated therewith, and therefore the elastic member may be excited in any number of directions depending on the operating frequency of the motor. Often, the vibratory process equipment requires the force to be applied in a single direction or degree of freedom, and therefore forces in the direction of any of the other degrees of freedom are undesirable, thereby detracting from the desired motion and reducing efficiency of the system.
In addition, vibratory process equipment using conventional rotating motors have a rotational inertia that delays stopping and starting of the equipment. As the rotating motors are accelerated from rest to the operating speed, the resulting vibratory force passes through various undesirable frequencies that may excite the connecting or isolation elastic members in undesirable directions. Still further, the vibratory force passes through the same undesirable frequencies as the motors decelerate from operating speed to rest. For example, specific frequencies may cause isolation bounce, isolation rock, and rocking between the drive and the bed, among others. These undesirable motions cause extraneous movement of the bed, which may be particularly undesirable for applications requiring quick starting and stopping, such as precision feeders.
While the following disclosure is susceptible to various modifications and alternative constructions, certain illustrative embodiments thereof have been shown in the drawings and will be described below in detail. It should be understood, however, that there is no intention to limit the disclosure to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the disclosure as defined by the appended claims.